With a total length of 215 miles (346 km), the Thames is the longest river entirely in England and the second longest in the United Kingdom. It rises at Thames Head in Gloucestershire, and flows into the North Sea at the Thames Estuary via London, the country's capital, where it is particularly deep and navigable; the Thames drains the whole of Greater London. Its tidal section includes most of its London stretch with a rise and fall of 7 metres (23 ft); tides reaching up to Teddington Lock. Along its course are 45 navigation locks with accompanying weirs. Its catchment area covers a large part of South Eastern and a small part of Western England and the river is fed by 38 named tributaries. The river contains over 80 islands. Having both seawater and freshwater stretches, the River Thames supports a variety of wildlife.
Human activity along points from its source to its mouth is evidenced for thousands of years in places; now it provides dwelling places, water power, food and drink. A major highway is formed for much of its length for shipping and supplies: through the Port of London for international trade, internally along its length and by its connection to the British canal system. The river’s strategic position has seen it at the centre of many events and fashions in British history, earning it a description by John Burns as “Liquid History”. It has been a physical and political boundary over the centuries and generated a range of river crossings.